*{
    padding: 0;
    margin: 0;
    vertical-align: baseline;
    -webkit-box-sizing:border-box;
    /*谷歌内核 */
    box-sizing: border-box;
}
/* 继承window */
html{
    height: 100%;
}
body{
    height: 100%;
    color:#fff;
    -webkit-perspective: 1000;
    perspective: 1000;
    background-color: #4444;
    background-image: -webkit-linear-gradient(top,#444444,#999999);
    /* position: relative; */
}
.book{
    width: 300px;
    height: 300px;
    position: absolute;
    left: 50%;
    top: 50%;
    margin-top: -150px;
    margin-left: 150px; 
    transform: rotateX(60deg) rotateZ(3deg);;
    user-select: none;
}
.front-cover{
    cursor: move;
    transform: rotateY(120deg);
    transform-origin: 0 50%;
}
.front-cover.back{
    background-image: url(https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=2050318681,1081448419&fm=26&gp=0.jpg);
    background-repeat: no-repeat;
    background-position:50% 50% ;
    
}
.page{
    width: 300px;
    height: 300px;
    padding: 1em;
    position: absolute;
    left: 0;
    top: 0;
    overflow: hidden;
}